Restoring the Stonehenge Landscape: using Lepidoptera as bio-indicators of biodiversity value and landscape connectivity

Habitat restoration at the landscape scale has the potential to restore connectivity to our fragmented landscapes. Colonisation of these restored habitats may however, be slow if restored sites take decades to reach the required ecological conditions (Fagan et al. 2008) and/or these sites are surround by land cover that are impermeable to the movement of organisms through them (Eycott et al. 2012).

As part of the Stonehenge World Heritage Site Management Plan, over 500 hectares of chalk grassland are currently being restored in Wiltshire, UK, using species-rich, locally sourced seed mixtures (Young et al. 2009). The aim is to re-connect the isolated fragments of ancient chalk grassland. The project provides an opportunity to investigate the ecological benefits of landscape restoration and the landscape factors and species traits that facilitate or impede the re-colonisation of target taxa.

In collaboration with the National Trust, field surveys were undertaken from 2010-2012 to record Lepidoptera as bio-indicators of restoration success and landscape permeability. Transect surveys were located within areas of different habitat type, age since restoration (Twiston-Davies et al. 2011) and across the edges of the chalk grassland fragments. In addition to this, edge permeability was measured as the proportion of Lepidoptera crossing chalk grassland fragment edges with adjacent land cover types of arable land and new restoration. Finally, we analysed the connectivity of the wider landscape as a consequence of the landscape scale restoration using the permeability values of different land cover types to conduct cost distance analyses in Arc View (version 10) (Eycott et al. 2011, Watts et al. 2010). These edge permeability and landscape connectivity analyses were conducted fo Lepidoptera species grouped as those more associated with short-grass herb-rich grasslands and tall-grass grasslands referred to as short-grass and tall-grass ecological groups respectively (Shreeve et al. 2001).

Transect surveys showed that restored grasslands can approach the ecological conditions of the target ancient chalk grassland habitat within 10 years with increasing species richness and the colonisation of Lepidoptera species in the tall-grass ecological group e.g. Maniola jurtina and Melanargia galathea (Meadow brown and Marbled white). Additionally, results suggest that even recent restoration as little as two years old may potentially reduce the functional isolation of ancient chalk grassland fragments, especially for species associated with short-grass habitats such as Lysandra bellargus and Polyommatus icarus (Adonis blue and Common blue). However, the ancient chalk grassland fragments showed higher Lepidoptera densities and diversity and some species with preferences for short-grass habitat such as Cupido minimus (Small blue), were restricted to ancient chalk grassland fragments and absent from restoration grasslands (Twiston-Davies et al. 2011).

Analysis on the connectivity of the landscape indicated that the grassland restoration may increase connectivity for Lepidoptera species in the tall-grass ecological group which could utilise the restoration grassland network. However the short-grass group may remain potentially isolated as these Lepidoptera, more associated with chalk grassland may require time for restoration grasslands to mature or targeted conservation.

These overall results suggest that quite rapid restoration success is achievable for some habitats, Lepidoptera species and ecological groups; however, they also show that additional management will be needed to assist the colonisation of the more specialist species in the future. Despite this, habitat restoration at the landscape scale is an effective, long term approach to enhance biodiversity and to restore landscape connectivity.